The importance of sex in science

In science, what difference does sex make? Dr. Joanna Bagniewska, ecologist, well-known science communicator and teaching fellow at the University of Reading, is here to explain.

I’m an ecologist – and ecologists talk about sex A LOT. We love to prod the underlying differences between sexes in different species. After all, why should we assume that males and females, which occupy different territories, have different diets and exhibit different behaviours, would be ecologically and evolutionarily identical?

Consequently, in the scientific articles in my field, the sex of study animals is reported on a regular basis. I was very surprised to find out, however, that this attitude is quite different in other disciplines, e.g. in biomedical research.

Until recently, in medical studies, female animals were treated simply as male animals with hormonal fluctuations. Such an oversimplification is, unfortunately, very often inappropriate and insufficient. Just last year a group of international researchers, led by scientists from McGill University, showed that when it comes to pain, not only is there a difference in tolerance and sensitivity between the sexes – there are also fundamental physiological differences in dealing with it. In rodents, the two sexes actually use different immune cells in the spinal cord to process the pain – T cells in females, and microglia in males. Yet, Jeffrey Mogil from McGill reports that only 3 out of 71 scientific articles published in the journal Pain in 2015 confirmed the use of experimental rodents of both sexes; almost 80% used only male animals. Research from UC Berkeley, led by Annaliese Beery, also showed a strong male bias in mammalian research in eight out of ten biological fields, most prominently in neuroscience. The authors suggest that studies focused solely on one sex should clearly indicate it in article titles.

There is a flip side of the coin, too – the sex of the researchers themselves. In 2014, a study led by Robert Sorge, found that mice and rats used in experiments react differently to male and female researchers. When exposed to the scent of male humans, the rodents become very stressed – so much so, that such strong stress acts as an analgesic. What does it mean? Rodents (of both sexes) handled by male researchers may be less sensitive to pain, and, as a consequence, the sex of the experimenter may lead to differences in baselines in behavioural studies, on which further applied research is then founded. Unfortunately, most of the time the sex of the researcher is not reported in publications, making comparisons between studies difficult, if not impossible.

Discoveries such as those mentioned above lead to questions about their future applicability: types of pain medicine developed, dosages trialled in pain studies, and relevance to human subjects. And while the American Congress has introduced the Research for All Act, requiring National Institutes of Health to run clinical trials on both men and women (in… 2015!), there is still a lack of consideration for sex in study animals, primary cells, or even cell lines.

Luckily the idea of gendered innovation, where gender and sex are incorporated into research principles, has been gaining recognition – largely due to the work of Londa Schiebinger of Stanford University. Thanks to this approach, it turned out that osteoporosis – historically considered a predominantly female disease – can have very serious consequences for males; conversely, heart disease is not just a male problem – but is diagnosed differently in females.

So… let’s talk about sex! Particularly in the context of good experimental design.